Geologic sequestration¹ (GS) of carbon dioxide (CO₂), a greenhouse gas (GHG), has been identified as one of several approaches to reduce atmospheric concentrations of CO₂, thereby contributing to the mitigation of climate change (IPCC, 2005). A large body of literature indicates that GS is a viable technology that can be conducted in a safe manner when coupled with a comprehensive approach to ensure protection of human health and the environment (see text box). Nonetheless, there are potential risks and uncertainties associated with GS. To systematically identify those conditions that could increase the potential for adverse impacts from GS, the U.S. Environmental Protection Agency (EPA) has developed a Vulnerability Evaluation Framework (VEF).